Controlling the rate of fuel dispensed to the cylinders, commonly referred to as throttle control, in diesel engines is accomplished by adjusting the output of the fuel pump. Throttle controls have evolved from a mechanical linkage directly connecting a foot pedal to the fuel pump, to an electronic linkage between the foot pedal and a computer, the computer then controlling the fuel pump.
Prior to the electronic inter-connection, a foot pedal was mechanically linked to the fuel pump and actuation of the foot pedal altered the output of fuel pumped by the fuel pump. The foot pedal was held in the home or idle position by a spring arrangement and the operator would merely depress the pedal to increase the fuel output of the pump thereby controlling the RPM and/or power output of the engine. The linkage of the pedal to the pump was proportional, the more the pedal was depressed, the more fuel was delivered to the cylinders. Fuel dispensing was then based purely on the demand of the operator.
The current trend in diesel engines is electronic control of the fuel pump output. The fuel pump is computer controlled and reacts to an input signal from the foot pedal. In the electronic or computer controlled system, the operator still utilizes a foot pedal. Instead of being mechanically linked to the pump, the pedal depression is monitored by a computer. The monitoring function is achieved through the use of a potentiometer. The potentiometer is rotated with depression of the pedal and provides an input signal to the computer.
The computer controls the fuel pump output based on input data from the potentiometer but it also factors in other data such as temperature, humidity, engine load, etc. to provide increased efficiency, economy of operation, and to reduce undesirable emissions to the atmosphere.
Initially the potentiometer was located in the engine compartment near the fuel pump. This was an undesirable arrangement due to the complex mechanical linkage required to connect the foot pedal to the potentiometer. The operating environment was also a problem in that it exposed the potentiometer to heat, oil and dirt that many believed caused premature failure of the potentiometer. The potentiometer was then incorporated in a foot pedal assembly structure that included a means for providing rotative motion of the potentiometer in reaction to depression of the pedal. This pedal assembly was floor mounted, and limited the design configuration and placement. Making adaptions to differing potentiometers that required a different degree of rotation created a major design change. At times, the modified design configuration required that operator convenience be compromised.